Split Speed Bump http://www.portlandonline.com/transportation/index.cfm?print=1&a=85... Split Speed Bump Kathy Mulder, PE, City of Portland, Oregon, Traffic Calming Program* January, 1998 Introduction History/Problem Test and Test Plan Conclusions and Recommendations Introduction Speed bumps have been found to be very effective at slowing traffic on residential streets throughout the City of Portland. City residents have embraced these devices as a means to slow traffic and enhance their livability. The speed bump programs began in 1992 after several months of test and evaluation with two bump designs. The 14 foot speed bumps, only used on Local Service Streets (the lowest classification of streets in the City), slow passenger cars and light vans so that the 85th percentile speed along the street is between 24 and 28 mph. The 22 foot speed bumps allow an 85th percentile speed of 29 to 34 mph. The Fire Bureau expressed concern that the 22' speed bumps are slowing their trucks and engines causing a negative impact on the Fire Bureau's 4 minute "fire response time"goal. In a series of several speed bumps on primary fire response routes, valuable time is lost, endangering public safety. We needed to develop a solution that would address both aspects of public safety, rapid response by Emergency Services and traffic calming for residential streets. History/Problem In 1991 the City of Portland Bureau of Traffic Management undertook a study of speed bumps (humps) in response to public demands for some respite from the excessive and continual increase of traffic speeds. As the result of two years of testing, speed bumps became a standard 'tool' for addressing the problem of speeding on Portland's residential streets. In Phase III of the original 1992 speed bump tests, the " Fire Bureau indicated a maximum comfortable speed of 20 mph for the 14'...speed bump and 25 mph for the 22'...speed bump". The 14' speed bump was adopted for local service streets that do not have transit or are not a primary fire response route. The 22' speed bump is designed for streets with high volumes of traffic, and those that are transit or primary fire response routes. The Traffic Calming Program has been installing speed bumps since 1992, and in the fiscal year 1995-96, installed more than 100 new speed bumps. With so many bumps installed, and hundred's of streets on waiting lists, the Fire Bureau and the Bureau of Traffic Management became concerned about a "cumulative effect", or how several speed bump streets along any emergency route may impact the response time. The goal of the Portland Bureau of Fire and Emergency Services is a response time of 4 minutes or less on 90% of emergency calls. A study was undertaken to quantify the effects of speed bumps on emergency vehicles. Measurements found that the amount of the time increase was dependent upon the type of vehicle and the type of traffic calming. Rescue vehicles were not slowed at all over the 22' bumps, while trucks and engines were slowed as much as 9 seconds per bump. It was decided that an "emergency response route" street classifications would need to be developed, similar to the City's existing traffic street classifications2, before any more traffic slowing devices could be placed on emergency response routes. This process of developing an emergency response route street classification and policies is a long and detailed task that can take several years to complete. All projects planned for streets currently used as primary routes by the Fire Bureau were put on hold until the classification process was completed. In the meantime, excessive vehicle speeds continue to threaten public safety and neighborhood livability, and a great number of speeding problems are found on streets that also serve as primary response routes. The Traffic Calming Program needed a device that would both accommodate the Fire Bureau vehicles, and still slow speeding motorists. 1 of 8 2/2/2012 3:10 PM Split Speed Bump http://www.portlandonline.com/transportation/index.cfm?print=1&a=85... Test and Test Plan Since fire and emergency vehicles are allowed, by law, to use any portion of the street they need when on an emergency response run, we began with the concept of a chicane using two halves of a 22' speed bump separated by enough distance so that the emergency vehicle with the least amount of maneuverability could go through the chicane at approximately 20 mph. Phase I A Traffic Calming engineer and a Fire Bureau battalion chief used cones to build a simulation of the test device at the Fire Bureau Training Center. The vehicle selected by the Fire Bureau for testing was the vehicle with the least amount of maneuverability. The truck was 39 feet long, 8 feet, 4 inches wide, with a wheelbase of 18 feet, 6 inches. The street width used was 40'. RESULTS OF PHASE I In August of 1996, trial runs were conducted in the Fire Bureau Training Center lot, in a wide area of asphalt. A street segment and speed bump halves were outlined with cones, and runs were made through the split bump halves. After several runs, it was decided that the distance between the two lane bump halves needed to be at least 28 feet for the vehicle to maneuver through at or near 20 mph. Preliminary drawings of the new device were made and a field test was planned. Phase II Part 1 An actual street test location was selected that was part of an existing traffic calming project: SE Market Street between SE 117th and SE 112th Avenues. This street is 42 feet wide, has no horizontal curves, and the visibility along the street is excellent. This segment of SE Market is defined by a signal at SE 112th and an all-way stop at SE 117th. Photos The nearby fire station was notified and asked to make a few practice runs through the off-set speed bump and offer any suggestions they felt were appropriate. The device was placed approximately 200 feet west of the all-way stop. The first part of the testing was for safety. Concerns of whether automobile drivers would violate the device and chicane between the bumps were raised. Twenty-four hour time lapse video equipment was placed to record driving patterns over the bump. Part 2 This part of the initial testing was to determine if, and how fast fire vehicles were able to drive around the two bump halves. The largest Fire Bureau vehicles from from the nearby station was used for the short test. Part 3 The final part of Phase II was to place another split speed bump device approximately 600 feet west of the original device to determine the effect on speeds the two devices have in combination. Total slowing effect on fire vehicles was tested. This was a controlled test that matched the original test that determined the time lost by speed bumps on fire vehicle response times. RESULTS OF PHASE II 2 of 8 2/2/2012 3:10 PM Split Speed Bump http://www.portlandonline.com/transportation/index.cfm?print=1&a=85... The 24 hour time-lapse video showed that drivers did not swerve into the oncoming lane to avoid the speed bump half in their lane. The temporary concrete medians and signs placed in advance of each bump half seemed to keep drivers in their own lane and over the speed bump. Dense centerline striping and raised reflective pavement markings gave an illusion that a median continued the entire distance between the bump halves. Subsequent 24 hour time-lapse video showed no indication of confusion on the part of the drivers, nor any violations of drivers trying to avoid the device at any time. The results of the Fire Bureau vehicle testing were favorable. The vehicles were able to travel through the "chicane" at 17 to 21 mph. They indicated that the speed was quite satisfactory, and that this maneuver is no different than weaving around cars. Concern was raised that a car may stop in the middle of the gap between bumps while the emergency vehicle approaches. There was fear that this device might prevent drivers from pulling off to the right when the emergency vehicles are running. Parking removal would alleviate this problem by providing an available refuge for cars pulling off to the right. If a car does stop in the middle of the device and blocks the fire vehicle pathway, the Fire Bureau decided that they would just go over the 22' bump. An occasional 22' speed bump does not create serious delay problems for them. It was determined that parking removal would be necessary for the Fire Bureau to perform the chicane maneuver. Parking was removed on both sides of Market Street opposite each bump half. Since it was found that the general public is willing to stay to the right of the centerline, two adjustments were considered to the companion device to be installed approximately 600' from the first device. The first adjustment was to make the approach islands shorter. It appeared that the "Keep Right" sign was enough to win driver compliance, and that the 20' island could be made smaller, just enough to place the sign. The second adjustment was to widen the gap between the two bump halves. This was done to explore how far apart the two bump halves can be and still maintain driver compliance on a straight stretch of street. With the second device in place (installed 4/11/97) the street was measured for overall slowing effect.